This invention relates to a class of fluorotelomers end-capped with secondary alcohols or their ethers or esters, to a process for producing the polymer, and to a process for using the polymer as insoluble, chemically and thermally stable lubricants, mold release agents, polishes, and coatings.
Wax-like fluorotelomers are disclosed in U.S. Pat. No. 3,067,262. Such fluorotelomers were based predominately on a fluorotelomer backbone of polytetrafluoroethylene (PTFE) formed by telomerization of tetrafluoroethylene (TFE) in 1,1,2,-trichloro-1,2,2-trifluoroethane (TCTFE) in the presence of a peroxide free-radical initiator wherein the TCTFE served both as a solvent and as a telogen. Telomerization can be defined as a reaction between two substances in which one substance provides the terminal groups (telogen) and the other provides the internal linkages of the telomer.
U.S. Pat. No. 5,552,500 and U.S. Pat. No. 5,665,838 disclose a process for producing a fluorotelomer in which a hydrochlorofluorocarbon is used both as telogen and solvent. The fluorotelomers, dispersed in 1,1-dichloro-1-fluoroethane (HCFC-141b), have been used commercially as dry film lubricants, and sold by E. I. du Pont de Nemours and Co. under the trademarks DryFilm DF and DryFilm 1000.
An international agreement in the 1980""s banned most uses for chlorofluorocarbons such as TCTFE and minimized over time the uses of hydrochlorofluorocarbons (HCFC) such as HCFC-141b, because of their threat to the ozone layer in the upper atmosphere and their involvement in global warming. U.S. Pat. No. 5,310,870 discloses a process for producing a fluorotelomer by reacting TFE or hexafluoropropylene with a hydrofluorocarbon telogen in solution, in the presence of a free radical initiator. This hydrofluorocarbon telogen consists essentially of an acyclic organic compound having a boiling point at atmospheric pressure between 25xc2x0 C. and 150xc2x0 C.
Many industrial operations require the use of release agents to reduce the tendency of a molded product to stick to the mold, or that of a tool to stick to the object on which it is working. In some cases, where a typical lubricant would be unsatisfactory or unsightly, e.g., a window frame, a release agent may also be used as a dry film lubricant to make it easier for a movable part to slide on a stationary piece of equipment. Release agents may be a solution, dispersion or solid, and typically form a thin, generally invisible film on one or both of the above touching objects.
For example, Japanese Kokai JP6-157614A discloses a polymerization process using 2,3-dihydro-decafluoropentane as polymerization medium; JP10-158335A discloses a fluoropolymer containing a hydroxyl group having a fluorine content of 20 weight % or more and a molecular weight of 500-1,000; U.S. Pat. No. 5,789,504 discloses a process for producing a low molecular weight polytetrafluoroethylene having a melting point of 250xc2x0 C.-325xc2x0 C.; and EP 0723979A1 discloses a comparable process wherein the solvent is selected from a group that also includes hydrofluorocarbons. However, these patents and applications do not disclose a process or composition for use as release agents or lubricants.
WO 98/51649 discloses a fluorinated saturated hydrocarbon containing 10%-95% of a trihydrofluorocarbon and useful as a solvent or forming a polymer coating to promote cleaning, lubrication or repellency on surfaces. Also U.S. Pat. No. 5,476,603 discloses a composition which is liquefied under pressure, and comprises certain non-polymeric hydrofluorocarbons and an agent having a releasing action selected from the group of certain waxy esters having 34 to 50 carbon atoms, a paraffin wax, a polyethylene wax and a metal soap.
There is a constant need for providing an improved release agents and lubricants that are environmentally friendly, i.e., not based on chlorine-containing fluorocarbons.
A composition, which can be used as, for example, mold release agent or lubricant, comprises a fluorotelomer comprising repeat units derived from a fluoroalkene, and optionally a comonomer, having an end group derived from a secondary alcohol or derivative thereof.
A process comprises contacting a fluoroalkene, and optionally a comonomer, in a hydrofluorocarbon, with a free radical initiator and at least one secondary alcohol or derivative thereof.
The composition comprising a fluorotelomer can be used as mold release agent. For example, a dispersion of the fluorotelomer in a solvent or water, when applied to a mold and solvent allowed to evaporate, provides a coating that affords multiple releases of an article from the mold. The coating can be used at temperatures ranging from ambient to over 300xc2x0 C.
The composition can also be used as lubricant. For example, a coating of the fluorotelomer applied to a surface will provide a very lubricious coating with a low coefficient of friction. The surface can be a mold or other object made of wood, metal, plastic, rubber, stone, cement, glass, or fiber. These surfaces are well known to one skilled in the art.
Any fluoroalkene that can produce a fluorotelomer having the property disclosed herein can be used. The preferred fluoroalkene monomer contains 2 to about 10, preferably 2 to 3, carbon atoms. Examples of suitable fluoroalkenes include, but are not limited to, 1,1 -difluoroethylene, 1,2-difluoroethylene, tetrafluoroethylene (TFE), 3,3,3-trifluoropropene, hexafluoropropylene (HFP), and combinations of two or more thereof. The most preferred fluoroalkene is TFE.
The preferred fluorotelomers are homotelomers, but a cotelomer (copolymer) containing repeat unit derived from a comonomer can also be produced. The comonomer is generally an ethylenically unsaturated compound, which can be fluorinated or perfluorinated. The amount of repeat units derived from a comonomer can be in the range of from about 0.1 to about 10, preferably 0.3 to 3.0 weight % of the copolymer.
Suitable comonomers include, but are not limited to, ethylene, propylene, butylene, decene, 1,1-difluoroethylene, 1,2-difluoroethylene, TFE, 3,3,3-trifluoropropene, HFP, and combinations of two or more thereof. The preferred comonomers are perfluorinated comonomers. The most preferred comonomer is TFE, HFP, or combinations thereof.
As disclosed below, a hydrofluorocarbon is used in a process for producing the fluorotelomer of the composition, a hydrofluorocarbon can also be incorporated into the fluorotelomer as an end group. The suitable hydrofluorocarbons include, but are not limited to, any of those disclosed in U.S. Pat. No. 5,310,870, the disclosure of which is incorporated herein by reference. Examples of suitable hydrofluorcarbons include, but are not limited to, 2,3-dihydrodecafluoropentane, perfluorobutyl methyl ether, perfluorobutyl ethyl ether, 2,4-dihydrooctafluorobutane, 1,1,2,3,3,3-hexafluoropropyl methy ether, 2-trifluoromethyl-2,3-dihydrononafluoropentane, 1,1,1,3,3-pentafluorobutane, or combinations thereof. These hydrofluorocarbons can be obtained commercially. For example, 2,3-dihydrodecafluoropentane is available from E. I. DuPont de Nemours and Co., Wilmington, Del. and perfluorobutyl methyl ether and perfluorobutyl ethyl ether are available from 3M Co., Minneapolis, Minn.
Generally, majority of the end group of the fluorotelomer can be derived from any secondary alcohol or derivative thereof. A suitable secondary alcohol or derivative thereof is the one that is substantially soluble in a hydrofluorocarbon disclosed herein. The most preferred secondary alcohols are those having at least 4 to about 12 carbon atoms and an xcex1-hydrogen. The end group can also be derived from a derivative of a secondary alcohol. The derivative of suitable secondary alcohol can include an ether or ester of a secondary alcohol or combinations thereof. Also suitable is the combinations of a secondary alcohol, ether thereof, and/or ester thereof. Examples of suitable secondary alcohols include, but are not limited to, 2-propanol, 2-butanol, 2-pentanol, 2-hexanol, 2-heptanol, sec-butyl acetate, cyclohexanol, 1-methoxy-2-propanol, 1-methoxy-3-butanol, 1-methoxy-2-pentanol, 1-methoxy-2-propanol acetate ester, and combinations of two or more thereof. Most preferred is 2-butanol, 2-pentanol, or combinations thereof.
The molar ratio of the repeat units derived from the fluoroalkene to the secondary alcohol or its derivative can be in the range of from about 18:1 to about 500:1, preferably about 120:1 to about 150:1. The molar ratio of the repeat units derived from the fluoroalkene to the hydrofluorocarbon can be in the range of from about 800:1 to about 2500:1, preferably about 2000:1 to about 2400:1.
As disclosed below, a free radical initiator is generally used in producing the fluorotelomer. Generally, a minor amount of the free radical initiator can also be incorporated into the fluorotelomer. The amount incorporated generally is about the same as, or lower than, that of the hydrofluorocarbon.
The fluorotelomer can have or comprise a structure depicted as either H(CX2)pBqDr or a mixture of H(CX2)pBq and H(CX2)pDr. In the formulae, X is H or F in which preferably xe2x89xa780%, more preferably xe2x89xa790%, and most preferably xe2x89xa799% is F; p is a number from about 36 to about 1500, preferred 60 to 600; B denotes any repeat units derived from a hydrofluorocarbon; q is a number from 0.02 to 0.4, D represents the end group derived from a secondary alcohol; and r is a number from 0.2 to 1.0.
According to the second embodiment of the invention, a process that can be used to produce a fluorotelomer, such as the one disclosed above, is provided. The process comprises, consists essentially of, or consists of, a fluoroalkene, and optionally a comonomer, in a hydrofluorocarbon as solvent, with a free radical initiator and at least one secondary alcohol or derivative thereof.
The fluortelomer that can be produced is the same as that disclosed above. The hydrofluorocarbon, secondary alcohol or derivative thereof, and comonomer are the same as those disclosed above.
Essentially any free radical initiator can initiate reaction to produce the fluorotelomers of this invention in the presence of a hydrofluorocarbon, fluoroalkene, and secondary alcohol. Preferred free radical initiators are di-tertiary butyl peroxide, tertiary-butyl perbenzoate, tert-amyl 2-ethyl hexanoate, and azo initiators such as 1,1-azobis(cyanocyclohexane) and most preferred is di-tertiary butyl peroxide. The amount of free radical initiator used preferably falls within the range of 0.4 to 3.0, more preferably 0.7 to 2.5, weight %, base on the weight of the fluoroalkene.
The amount of secondary alcohol can be that which produces a fluorotelomer with a number average molecular weight in the range of from about 1,800 to 75,000, preferably 3,000 to 30,000. For example, the amount of secondary alcohol can be between about 0.1 to about 5, preferably about 0.3 and about 5, and preferably 2.5 to 4.0 mole %, based on the total number of moles of fluoroalkene.
The fluorotelomer having an end group derived from a secondary alcohol or derivative thereof can allow the fluorotelomer for crosslinking with a crosslinking agent. Suitable crosslinking agent include a tetraalkyl titanate having the formula of M(OR)4 where M is titanium or zirconium and each R is independently an alkyl radical, a cycloalkyl radical, an aralkyl hydrocarbon radical, and combinations of two or more thereof in which each radical can contain, preferably, 2 to 12 carbon atoms per radical and each R can be the same or different. Suitable tetraalkyl titanates include, but are not limited to, tetraethyl titanate, tetrapropyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, tetra-2-ethyl titanate, tetraoctyl titanate, tetraethyl zirconate, tetrapropyl zirconate, tetraisopropyl zirconate, tetra-n-butyl zirconate, tetra-2-ethyl zirconate, tetraoctyl zirconate, and combinations of any two or more thereof. The preferred crosslinking agents include, but are not limited to, TYZOR(copyright) TPT and TYZOR(copyright) TBT (tetraisopropyl titanate and tetra n-butyl titanate, respectively) available from E. I. du Pont de Nemours and Company, Wilmington, Del. Crosslinked fluorotelomers generally have enhanced bonding, compared with those non-crosslinked ones, to the surface of a substrate, which can be made of wood, metal, plastic, rubber, stone, cement, glass, fiber, and combinations of two or more thereof.
The process, a telomerization, can be carried out at temperatures in the range of about 100xc2x0 C. to about 200xc2x0 C., preferably about 110xc2x0 C. to about 180xc2x0 C., and most preferably 120xc2x0 C. to 160xc2x0 C. at autogenous pressures. The pressure can range from about 100 to about 700 psig, preferably about 400 to about 600 psig, and most preferably about 500 psig. The preferred time period is about 1-6 hours, though it can be shorter or longer than this range. In a continuous flow reactor the reaction can proceed for about 1-2 hours. A batch process can be preferably carried out at an autogenous pressure with temperatures in the range of about 125xc2x0 C. to about 160xc2x0 C. for about 4-6 hours. The molar ratio of hydrofluorocarbon to fluoroalkene can be in the range of from about 1:1 to about 10:1, preferably 2:1 to 8:1. Generally the higher the ratio, the lower the telomer molecular weight.
After the telomerization process, the fluorotelomer is generally recovered as dispersion in the hydrofluorocarbon. The dispersion can contain from about 5-20 weight % of the fluorotelomer, with dispersions of high molecular weight fluorotelomers falling at the low end of this range. If desired, the fluorotelomers can also be exchanged into other solvents such as isopropanol or in water as well.